The present invention relates to an artificial respirator. Such an artificial respirator is one of a type of medical treatment equipment allowing a flow of vapor through the respiration circuit in response to a patient's respirations. Since this unit is directly connected to the human body, extreme care should always be execercised to ensure its safe operation. As a safety measure, it is extremely important to ensure prevention of even the slightest interference in respiration under any circumstance during use. More specifically, if for any reason the respiration circuit allows its vapor level to rise beyond a critical level, the respiration circuit should be instantly released in order to decrease the vapor pressure level. Conventional respiration devices made provide a relief valve for ensuring its safe operation. However, when applying a relief valve alone, the respiration valve must be operated at the same time by operating another drive means, and as a result, the safety mechanism is unavoidably complex.